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Mate guarding and male mate choice in the chameleon grasshopper Kosciuscola tristis (Orthoptera: Acrididae) Peter C. Mahoney, Nikolai J. Tatarnic, James C. O’Hanlon & Kate D. L. Umbers Journal of Ethology ISSN 0289-0771 J Ethol DOI 10.1007/s10164-017-0509-9 1 23 Your article is protected by copyright and all rights are held exclusively by Japan Ethological Society and Springer Japan. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your article, please use the accepted manuscript version for posting on your own website. You may further deposit the accepted manuscript version in any repository, provided it is only made publicly available 12 months after official publication or later and provided acknowledgement is given to the original source of publication and a link is inserted to the published article on Springer's website. The link must be accompanied by the following text: "The final publication is available at link.springer.com”. 1 23 Author's personal copy J Ethol DOI 10.1007/s10164-017-0509-9 ARTICLE Mate guarding and male mate choice in the chameleon grasshopper Kosciuscola tristis (Orthoptera: Acrididae) 1 2,3 1 Peter C. Mahoney • Nikolai J. Tatarnic • James C. O’Hanlon • Kate D. L. Umbers4 Received: 4 October 2016 / Accepted: 6 February 2017 Ó Japan Ethological Society and Springer Japan 2017 Abstract In the wild, male chameleon grasshoppers Introduction (Kosciuscola tristis) are frequently observed mounted on the back of females even when not in copula, and will fight Mate guarding, where males establish a close association off other usurping males. If this behaviour is mate guarding with a female either before or after mating, is a common and and reflects investment in male mate choice, then we effective strategy to avoid sperm competition (Alcock 1994; expect males to preferably guard females based on reliable Simmons 2001). It can occur where paternity benefits out- cues of quality. Cues for female quality likely include weigh the costs involved including time (e.g. Jarrige et al. female size and egg development that together may indi- 2016), energy (e.g. Elias et al. 2014), lost mating opportu- cate fecundity. We investigated male mate choice in the nities with other females (Parker 1974) and challenges from field expressed as mate-guarding preference, by comparing other males (e.g. Umbers et al. 2012). Pre-copulatory mate size and egg development in guarded and unguarded guarding allows males to secure future mating opportunities females. We found no difference between guarded and yet presents a risk as it requires investment before copulation unguarded females in measures of fecundity or body size. has occurred. As such, it is expected to occur where paternity The majority of females sampled did not contain any viable is driven by first male sperm precedence (Parker 1974; eggs. This finding suggests that male K. tristis indiscrimi- Grafen and Ridley 2004) or where it can reduce the likeli- nately guard females in a scramble mating system. hood of female re-mating (e.g. Elias et al. 2014). By guarding mates post-copula, males reduce the likelihood of Keywords Sexual selection Á Mating behaviour Á Alpine female re-mating and potentially achieve paternity through biology Á Sperm competition last male sperm precedence (Parker 1974). Given that mate guarding can involve ‘opportunity costs’, males should be selective as to which females they choose to guard (Parker 1974; Bonduriansky 2001). Male mate choice manifests in many forms including selective courting, male–male competition (display or combat), variable allocation of sperm, and mate guarding & James C. O’Hanlon (Parker 1974; Amundsen and Forsgren 2001; Bonduriansky [email protected] 2001; Reinhold et al. 2002; Edward and Chapman 2011). It 1 Department of Biological Sciences, Macquarie University, is expected to occur in systems where costs of mate search North Ryde 2109, Australia or assessment are low, female variability is high, and male 2 Department of Terrestrial Zoology, Western Australian investment in reproduction is high (Bonduriansky 2001). Museum, Welshpool 6986, Australia Mate choice by males has been less represented than female 3 Centre for Evolutionary Biology, School of Animal Biology, choice in the literature, but has attracted significant interest University of Western Australia, Crawley 6009, Australia in recent decades (e.g. Bonduriansky 2001; Gaskett et al. 4 School of Science and Health, Western Sydney University, 2004; Preston et al. 2005; Barry and Kokko 2010; Dough- Locked Bag 1797, Penrith, New South Wales 2751, Australia erty and Shuker 2014). While studies of male mate choice 123 Author's personal copy J Ethol are becoming more common, such choice tests are typically winter snowfall (June), and eggs overwinter in the soil conducted in laboratory environments. Field studies also (Green and Osborne 1994; Umbers et al. 2013). Solo males, offer valuable insights and may yield different results from solo females, and pairs where males are guarding females laboratory studies (Dougherty and Shuker 2014); For are all regularly observed in the field. Females are almost example, laboratory experiments with house finches (Car- always guarded by a male when they oviposit (Umbers podacus mexicanus) found that males selected for females et al. 2012). Males remain mounted during female ovipo- with bright plumage, but subsequent field studies revealed a sition, and additional males surround the pair and attack the strong, and previously undetected, role of female age in mounted male, whilst nearby non-ovipositing females male mate choice (Hill 1993). appear to be ignored (N.J.T. personal observation). Here, we investigate mate guarding in the chameleon grasshopper (Kosciuscola tristis) (Orthoptera: Acrididae) Data collection in the field. Chameleon grasshoppers are endemic to alpine regions of south eastern Australia (Umbers 2011; Tatarnic Sexually mature female K. tristis (n = 129) were collected et al. 2013; Slatyer et al. 2014) and exhibit characteristics from Dead Horse Gap (36°31.0320 S, 148°15.8970 E) near common to other insect groups where male mate choice Thredbo, NSW (9 am–3 pm, 3 April and 11 May 2012). occurs. Males and females occur in high densities, so costs When collected, females were either mounted by a male of mate search should be low. Male investment in repro- (n = 65) or not (n = 64). Females were not collected if duction appears to be high, as males are often observed they were mating or ovipositing at the time of sampling. guarding females by mounting on their backs for extended All females were frozen within four hours of collection and periods of time without copulation (K.D.L.U. personal kept at -20 °C until dissection. Because many specimens observation). Furthermore, males guarding females are were missing one hind leg at the time of collection (com- challenged for their position by other males, resulting in monly observed in the field), all specimens with two legs ferocious and damaging contests (Umbers et al. 2012). were weighed (JS-VG20 digital scale, Jennings Scale Whether this apparent guarding behaviour represents Company, Phoenix, USA) with one randomly chosen hind pre-copulatory or post-copulatory guarding is unknown. leg removed. We measured size (pronotum length and The mating system of K. tristis has not received significant width) using digital callipers (Sontax Australia). To research attention, and whether males are selective in their investigate whether males may be responding to female choice of females, or whether sperm precedence patterns mass relative to her body size, we calculated an index of occur, is also unknown. To test whether males exhibit body mass as the residual values of the linear relationship preferences for females in the wild, we compared the traits between pronotum length and body weight (herein referred of females that were guarded by males with those of females to as body mass index). Females were dissected and classed that were not guarded. As guarding a female represents a as either gravid or non-gravid. The eggs were counted and significant investment by males, we hypothesised that there removed, and weighed for total egg mass. would be a difference between guarded females and We were unable to collect data on the males that were unguarded females and that this difference may ultimately guarding the females, as upon approaching mounted pairs, confer a fitness advantage to the males. If males are pref- males would frequently jump off the backs of females into erentially guarding more fecund females, then we predict nearby vegetation. We were then unable to identify these that guarded females would be larger (Bonduriansky 2001; males amongst others, as K. tristis are abundant and occur Edward and Chapman 2011) and have greater egg mass than in high densities, making tracking individual males by eye unguarded females. Alternatively, if males gain fertilisation impossible. success through first male precedence (Simmons et al. 1994), males may preferentially guard non-gravid or lighter Data analysis females, as this may indicate early stages of egg develop- ment and a lower chance that the female has already mated Data were initially explored using factorial binomial (Butlin et al. 1987; Bonduriansky 2001). models to test for differences between guarded and unguarded females. However, this resulted in significance levels that were difficult to interpret and likely to be type I Materials and methods errors. We manually inspected the data to remove variables with high levels of co-linearity, and attempted to use for- Study species ward and backward stepwise methods to build a model. This did not remove issues with apparent false positives, Adult K. tristis emerge in late January, and egg laying nor did it improve models based on Akaike information typically begins in late February. Adults die with the first criterion (AIC) values. These issues, and a relatively low 123 Author's personal copy J Ethol sample size for multiple logistic regression methods, meant 0.8 that a factorial model approach was deemed inappropriate.

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